Renewable energy generation from wind power is currently of great interest. Large wind turbine generators are desired for offshore applications. Units in sizes exceeding 20 MW are of interest [1]. The generator’s physical size and efficiency are the two most important attributes whereas the mass is of less importance as the overall tower structure is driven by the wind momentum. Superconductors could play an important role in reducing the size and increasing the efficiency. The smaller physical size will permit shipping of the complete generator from the factory to the site. Initially, field excitation coils could be constructed using superconductors with a stator employing conventional conductors. Both rotor and stator coils could be constructed to enable quick replacement of defective coils to minimize down time. Inclusion of AC/DC converters within each stator coil could be considered. The low generator frequency could also permit use of superconductors for the stator coils. This is likely to have significant beneficial impacts on the size and efficiency of the generator. Compared to the conventional conductor stator, a superconducting stator potentially offers 30% reduction in overall diameter, 60% reduction in mass, and 1.5% increase in efficiency. At the low frequency, it might even be possible to consider striated REBCO conductors in the form of Roebel cables. However, the generator cost will be a strong function of the price of superconductors.
Wind power is also being considered for production of green hydrogen (H2) using electrolysis [2]. If liquid hydrogen (LH2) is considered for energy storage, then it could be used for cooling the superconducting windings. Thus, it might be possible to design very large units dedicated to production of H2 alone – avoiding transfer of electric power to the shore. This decouples the generator from the electric grid and allows optimizing the generator design for hydrolysis only. Hydrolysis requires DC that can be obtained simply by rectifying generator produced AC to DC. The electronics system needed for simple AC to DC conversion would be much simpler and cheaper than AC synched to the electric grid. The electronic system could also be operated at cryogenic temperature by embedding in each stator coil to provide output as DC for hydrolysis. For example, a 25 MW unit could be a self-contained facility for generating H2. This paper describes concept designs for 25 MW generators with hybrid and fully superconducting options. Offshore H2 production is estimated to be the most economical option [3].
[1] Garrett E. Barter, Latha Sethuraman, Pietro Bortolotti, Jonathan Keller, David A. Torrey, “Beyond 15 MW: A cost of energy perspective on the next generation of drivetrain technologies for offshore wind turbines”, Applied Energy, Vol. 344, 15 August 2023, 121272, https://doi.org/10.1016/j.apenergy.2023.121272
[2] Ashish Sedai, Rabin Dhakal, Shishir Gautam, Bijaya Kumar Sedhain, Biraj Singh Thapa, Hanna Moussa and Suhas Pol, “Wind energy as a source of green hydrogen production in the USA”, Clean Energy, 2023, Vol. 7, No. 1, 8–22, https://doi.org/10.1093/ce/zkac075
[3] Alessandro Singlitico, Jacob Østergaard, Spyros Chatzivasileiadis, “Onshore, offshore or in-turbine electrolysis? Techno-economic overview of alternative integration designs for green hydrogen production into Offshore Wind Power Hubs”, Renewable and sustainable energy transition, 2021, Vol.1, p.100005 https://doi.org/10.1016/j.rset.2021.100005
This work was supported by the New Zealand Ministry of Business, Innovation and Employment under the Advanced Energy Technology Platform program 'High power electric motors for large scale transport' Contract Number RTVU2004.